Generally speaking, there are two basic techniques for introducing injectable medicament into the spinal area of a patient. The techniques both can be used to create spinal anesthesia, one being delivery of the medicament into the epidural space, "epidural," and the other, penetration of the dural membrane with delivery of the medicament into the subarachnoid space, "spinal" or "subarachnoid." The medicaments can be any type of liquid therapeutic material including antibiotics, steroids and the like, but generally are agents used for anesthesia and analgesia. When the liquid medicament is an anesthetic agent, a subarachnoid placement is recognized as providing a faster, more uniform distribution, but several major side effects may result from an improper subarachnoid placement. These side effects may include nerve damage, either from contact with the needle or from high local concentrations of the medicament, pooling or inadequate mixing of the medicament in the cerebrospinal fluid.
Delivery of the medicament into the subarachnoid space requires a penetration depth of several centimeters. Puncture of the dural membrane for introduction of a needle or catheter with a large gauge needle may result in postoperative leakage of cerebrospinal fluid from the puncture site, often resulting in severe postoperative headaches. Thus, when puncture of the dural membrane is made with a needle, the smaller the size of the puncture the lower the probability of post-procedural leakage of cerebrospinal fluid. Small diameter needles of the length required to enter the subarachnoid space are quite flexible and as a result, difficult to accurately position when making penetrations to a depth of several centimeters. Practitioners have recognized the need to use a needle with sufficient stiffness to make the initial penetration and the need to use a small diameter needle for penetration of the dural membrane. This recognition has evolved into the use of an eight to ten centimeters long, larger diameter (ca. 16-18 gauge) introducer needle to enter the epidural space followed by the use of the bore of the introducer needle to place a longer, i.e., twelve to sixteen centimeters long, smaller diameter (ca. 22-28 gauge) spinal needle adjacent to and then to penetrate the dural membrane. The spinal needle is then used to administer a bolus of the anesthetic agent. The bolus results in rapid onset of anesthesia, and depending upon the placement and the amount administered, the effect may last several hours.
Correct placement and delivery of a subarachnoid inedicament is recognized by practitioners as being one of the more technique sensitive procedures currently practiced. There is considerable anatomical variation between patients related to the patient's size and weight. The practitioner generally positions the introducer needle between the vertebrae into the epidural space against the dural membrane, then advances the spinal needle through the dura into the subarachnoid space. Accurately perceiving when the dura has been penetrated is often difficult for the practitioner. There are several widely practiced techniques to confirm that the needle has entered the subarachnoid space. Some practitioners depend upon feeling a "pop" as the spinal needle penetrates the dura. Other practitioners routinely place a drop of fluid on the proximal hub of the spinal needle and depend upon observing the drop being drawn into the hub when the dura is penetrated. Many practitioners also often confirm that the subarachnoid space is penetrated by using the spinal needle to withdraw a sample of cerebrospinal fluid.
A survey of previous patent literature reports in this general area is found in U.S. Pat. No. 5,085,631. The patent discloses a method for placement of a subarachnoid catheter that utilizes a three component apparatus comprising an outer needle, an inner needle and a catheter intermediate the two needles.
A recent U.S. Pat. No. 5,480,389, discloses a regulating device for adjusting the length of a combined spinal epidural needle and the method of practicing its use. The disclosed invention utilizes standard commercially available spinal and epidural needles, providing a fixture for preselecting the spinal needle projection with respect to the epidural needle when the spinal needle is coaxially placed within the epidural needle. While this regulating device and method is quite useful in the practice of combine spinal epidural medication, the use of this device adds an additional item to the procedure kit, and additional manipulations.
Another recent U.S. Pat. No. 5,584,820, discloses a set for spinal anesthesia that has a hollow introducer needle, a spinal needle introducible through the introducer needle into the subarachnoid space, a stylet extendable through the spinal needle and an enlongate hollow sleeve. The disclosed hollow sleeve has a first hollow portion extending into the interior of the introducer needle and a second hollow portion extending longitudinally from the first hollow portion over the spinal needle only. The hollow sleeve is provided with a perpendicular screw disposed to be advanced against the cannula of the spinal needle to retain the spinal needle in a fixed position with respect to the introducer needle. The impingement of the perpendicular retaining screw directly upon the cannula of the spinal needle may result in particulate generation or damage to the small diameter spinal needle. Additionally, a gloved practitioner may have difficulty manipulating the necessarily small retention screw while holding the needles at the desired position.
Subarachnoid placement of medicaments, if done properly, is acknowledged to be desirable. Thus, a device and a method for its use that would minimize the size of the puncture of the dural membrane, allow accurate and controlled placement of a therapeutically effective amount of a medicament within the subarachnoid space, thereby reducing the potential for nerve damage, coupled with an ability to rapidly initiate and maintain a therapeutic level of the medicament for longer procedures would represent an advance to the medical arts. A method and apparatus that addresses these needs constitute the present invention.